Artificial antenna



Aug 8, 1944 M. CAwL-:IN Y 2,355,275

ARTIFICIAL ANTENNA Filed Feb. 25, 194s HG2 o v R. F. osclLLAToR L POWER AMPLIFIER MODULATOR INVENTOR Patented i Aug. 8, 1944 UNITED STATES PATENT GFFICE ARTIFICIAL' ANTENNA Madison C awein, Fort Wayne, Ind., assigner to Farnsworth Television and Radio Corporation, a. corporation of Delaware ApplicationFebruary 25 1943, Serial No. 477,049

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C takenv in connection wlththeiseveraliigures of This invention relates to Areactive networksand particularly to networks simulating the electrical characteristics of transmitting and receiving antennas.

According toconventional practice, there have been devised numerous arrangements of resistors, inductors and capacitors to simulate various signal transmission media. Such networksvare designed to provide, in compact form, apparatus having substantially the same electrical characteristics as real transmission media such as line wires, aerial or submarine cables and the like. ISuch apparatus is well suited for use in laboratories in connection with the design and testing ofv signalling apparatus to be employed with a particular transmission medium.

As is Well understood in the art, the design of certain types of radio transmitting and receiving apparatus is determined, in large part, by the antenna with which it is to operate. Frequently, especially when Working indoors, it is not convenient to erect such an antenna. It, therefore, is desirable to have available, in compact form, an articalantenna which has electrical characteristics closely approximating those of the real antenna with which the apparatus is to be used throughout the range of frequencies in which the apparatus is to operate. -Such an artificial antenna may be used to maintain a load on the output circuit of a. transmitter while it is connected for operation but is not radiating. It also is useful in measuring the energy output of a transmitter in the testing laboratory.'

An object of the present invention, therefore, is to provide a compact network of circuit elements proportioned and arranged to simulate the electrical characteristicsof an antenna over a range of frequencies including its first series resonant and parallel resonant frequencies.

Another object of the invention is to provide a reactive network which may be adjusted easily to simulate the electrical characteristics of any one of a large number of different antennas.

In accordance with the instant invention there is provided a network comprising a capacitance connected in parallel with a series arrangement of an inductance and a second capacitance. The value of one capacitance is substantially equal to that of the real antenna, while the value of the other capacitance and the inductance are substantially equal to 1/3 of the real antenna capacitance and inductance, respectively.

For a better understanding of the invention,

III

` capacitor 8.

together with other and further objects thereof,

reference is had to the following description 'adjustable capacitor 9.

the nductor 1 is adjusted to the accompanyingdrawing, andfits'scope Fig. 2 is an exterior view of' a housing: for the apparatus; and,

Fig. 3 is a fragmentary view of one arrange-vv ment of the capacitors.A

Referring now more particularly to Fig. 1, there is shown a radio transmitter comprising an oscillator l for generating a carrier wave of any frequency within a predetermined range of' frequencies. The carrier wave may be modulated in a conventional manner by a modulator 2. The modulated carrier wave is amplified by a radio frequency power amplifier 3.- The output of the ampliier is connected to the primary winding of an output transformer 4 in series with a` current measuringdevice such as a milliammeter 5. The secondary winding of the output transformer is connected to a reactive network S which consists of a series-parallel arrangement of an inductor and two capacitors proportioned and arranged to simulate the electrical characteristics of an antenna which is resonant at a frequency within the range of frequencies of the carrier wave. l

The network 6 comprises an adjustable inductor 1 connected in series with an adjustable This series arrangement is connected across the secondary winding of the output transformer 4 and is sh'unted by a parallel .The series capacitor 8 is adjusted to have a value which is substantially equal to the capacitance of the real antenna.

.The parallel capacitor 9 is adjusted to have a valuewhich is substantially equal to 1/3 of the capacitance'of the real antenna. The value of be substantially equal to 1/3 of the inductance of thereal antenna. The values of the inductance and capacitance of the real'antenna may be calculated l from the dimensions of the wire forming the antenna in the manner set forth in Circular C-74 of the National Bureau of Standards.

'Ihe impedance of the network 6 is represented by the expression ZFJ... (4'00-:155005200/3) where Za is the impedance of the artificial antenna, Lo is the inductance of the real antenna,

and Co is the capacitance of the real antenna. Y

is represented by the following expression Parallel resonance of the network occurs at a frequency where the angular velocity of the wave is represented by the following expression l 3 ca -2 LOCO The reactance of a real antenna may be simu= lated by such a network from zero frequency up to a frequency which is equal to the linear velocity of the wave divided by twice the length of the real antenna wire. Such a range of frequencies includes the fundamental, quarter wave-length and half wave-length resonant frequencies of the antenna. A

A network in accordance with this invention is particularly useful when the circuit elements are made adjustable so that the network may be made to simulate the electrical characteristics of any one of a large number of dierent antennas To this end the components of the network are mounted in a housing it of Fig. 2. The connections to the network are made through a pair of binding posts li mounted on one face ofthe housing lll. The value of the inductor l is varied by means of a control knob i2. Since the value of the capacitor 9 is always t/s oi the value of the capacitor S, these two elements may be arranged for simultaneous adjustment by suitable gauging o the respective capacitors. The adjustments are made by means of a control knob i3. The control kn'obs l2 and le are provided with suitably graduated scales and are mounted on one aceoi the housing lll.

Fig. 3 illustrates 9, typical arrangement ior ganging the capacitors 8 and 9 for simultaneous adjustment. The plates of the capacitors are assumed to be identical, and the capacitor 8 is provided with three times the number of plate elements that are provided for the capacitor 9. The rotor plates of the respective capacitors are mechanically connected to a shaft le to which is rigidly attached the control knob I3.

Referring now to the operation of the illustrated system utilizing an artificial ant/enna in accordance with the present invention, the frequency of the oscillator l may be varied by conventional meanssuch as a variable condenser i6, throughout the range of frequencies as hereinbefore defined. The power output of the transmitter, which may be expected to be transferred to the real antenna at any frequency, is indicated by the milliammeter E. Thus, the circuit components of the transmitter may be adjusted sultably for the transfer of the predetermined amounts of energy to the real antenna system with which the apparatus is to operate.

The reactive network 8 is adjusted to simulate the electrical characteristics of the real antenna, after first calculating the values of the inductance and capacitance of the real antenna in the manner described. The control knob I2 is set in accordance with the calculated value of the real antenna inductance. Also, the control knob i3 is setin accordance with the calculated value of the capacitance of the real antenna. It is seen that escasas y e will be substantially equal to the full capacitance and Ve of the capacitance of the real antenna.

When it is desired to simulate the characteristics of other antennas, it is merely necessary to Y' calculate the values of the inductances and capacitances thereof and to set the control knobs l2 and la in accordance with the calculated values.

While there has been described what at present is considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modications may be made therein without departing fromthe invention, and, therefore, it is aimed in the ap pended claims to cover all such changes and modifications as fall within the true spirit an scope oi' the invention.

What is claimed is:

l. A network to simulate the electrical characteristics of an antenna over a band of frequencies including the quarter wave-length and half wave-length resonant frequencies of said antenna comprising, a series arrangement of a capacitance and an inductance, and a capacitance connected in parallel with said series arrangement, one of said capacitances being equal to the capacitance of said antenna and the other of said capacitances and said inductance, respectively, being substantially equal to 1/a of the capacitance and inductance of said antenna.

2. A network to simulate the electrical characteristics of an antenna over a band of fre quencies including the quarter wavelle'ngth and half wave-length resonant frequencies of said antenna comprising, a series arrangement of a capacitance and an inductance. said capacitance being equal to the capacitance of said antenna, and said inductance being equal to l/3 of the inductance of said antenna, and a capacitance equalto V3 of the capacitance of said antenna connected in parallel with said series arrangement.

3. A network to simulate the electrical characteristics of an antenna over a band of frequencies including the quarter wave-length and half wave-length resonant frequencies oi said antenna comprising, a series arrangement of a capacitance and an'inductance, and a capacitance connected in parallel with said series arrangement, said series capacitance being equal to the the network then will simulate the characteristics 'I6 capacitance of said antenna, and said inductance and said parallel capacitance being equal to the same fractional parts of said antenna inductance (Lo) and capacitance (Co) respectively, whereby the impedance of said network is represented by the expression 3 LOOM-02 J w (400 LC0w2C0/3 4. A network to lsimulate the electrical characteristics of an antenna over aband of frequencies including the quarter wave-length and half wave-length resonant frequencies of said antenna comprising, a series arrangement of a capacitance and an inductance, a capacitance connected in parallel with said series arrangementI means for adjusting the value of said inductance to a value substantially equal to 1/3 of theinductance of said antenna, and means for adjusting the value of said series capacitance to substantially the capacitance of said antenna and the value of said parallel capacitance to substantially 1/3 of the capactanceof said antenna.

5. A network to simulate the electrical characteristics of an antenna over a band of frequencies including the quarter wave length and half wave length resonant frequencies of said 5 Vantenna comprising, a series arrangement of a capacitance and an inductance, a capacitance connected in parallel with said series arrangement, means for adjusting the value of said inductance to a value substantially equal to 1/3 of the calculated value o1' the inductan'ce of said antenna, and means for adjusting simultaneously the value of said series capacitance to substantially the calculated value of the capacitance of said antenna and the value of said parallel capacitance to substantially 1/3 of the' calculated value of the capacitance of said antenna.

MADISON CAW'EIN. 

